This invention relates to a method of operating automatic mold part producing apparatus for continuous casting apparatus comprising a mold chamber which, on one side, is closed by a pressure plate or pattern board that reciprocally is displaceable in the axial direction and, on the other side, by a counterpressure plate or pattern board which, for preference, remains stationary during the pressing operation. Through one or more passage apertures the chamber communicates with a supply bin for sand or similar mold forming material which is forced into and fills the mold chamber and subsequently is compressed by the movement of the pressure plate towards the counterpressure plate.
A machine of this type for automatically producing mold parts is disclosed by Jeppesen U.S. Pat. No. 3,008,199. In practice, the mold chamber of this machine is, in its top and/or side walls, provided with one or more slots through which the sand from the supply bin is forced into the mold chamber, for instance, by means of centrifugal impellers or by the use of pressurized air.
When pressurized air is used for this purpose, the supply bin, after having received the requisite quantity of sand, is hermetically sealed off from the surroundings. Following this, the upper part of the supply bin is connected to a pressurized air tank so that the air pressure will force the sand into the mold chamber until it is filled.
When using the prior art apparatus it has been found that the compactness or density of the sand in the filled mold chamber decreases in the vertical direction and that this variation of the compactness changes only negligibly in the course of the subsequent pressing operation. This is connected with the circumstance that the sand possesses a very low degree of flow. The varying compactness of the sand has the effect that the pressure plate which, normally, rests on the bottom of the chamber, tends to rise slightly therefrom during the compressing movement whereby the precision of the mold parts produced is adversely affected. Moreover, by the termination of the compressing movement, portions or fractions of the mold part formed may be torn off as the pressing plate, during this phase, will again sink down into abutment against the bottom of the mold chamber.
In addition, the varying compactness of the sand results in a varying resilience in the mold part when relieved from pressure by the backward motion of the pressure plate. As a consequence thereof, the pressure-relieved mold part will have a slightly greater thickness at the bottom than at the top and, when assembling a series of such mold parts so as to form a coherent string of molds, it will not in all circumstances be possible to ensure the desired tightness at the contact faces between the individual mold parts.